Polycarbonates are useful in a wide variety of applications in view of its good balance of properties, such as practical impact resistance, glass-like transparency, and moldability. In injection molding applications, effective mold release is a key property to enable efficient processing into formed articles. As such, a lower release force during the demolding of the parts is desirable. The lower release force can be achieved by adding a mold release agent to the thermoplastic composition. The release agent also helps to provide consistent processability.
Several materials, like polyesters, have the desired release performance. However, these materials have inferior mechanical properties, such as impact performance, compared to polycarbonate polymers. Further, these materials are difficult to process, as they have limited thermoformability for sheet applications and/or inadequate melt flow for injection molded parts.
An appropriate mold release not only facilitates processing, but should also be stable and inert during processing in such a way that it will not react with the polymer and other components, as well as preventing discoloring in time due to degradation. An appropriate mold release agent should not form deposits on the surface of the mold during injection molding nor on the roll calendar during extrusion processes and, therefore, become visible on the surface of the part causing aesthetic defects. Also, the additive should maintain transparency when required.
Conventional mold release agents, such as pentaerythrityl tetrastearate (PETS), provide acceptable release behavior in some applications. However, the release behavior is often not sufficient for relatively large parts or difficult profiles. The inadequate release behavior results in irregular processing or high release forces, possibly resulting in distortion of the ejected parts.
Further, it has been observed that polycarbonate profiles, during extrusion, can be affected by plate-out and vibrations can appear on the surface, generating issues on the overall product quality. Certain additive types have been found to be the root cause of these issues.
Processability and color stability/weatherability after extrusion are optimized by the use of some additives in the polycarbonate composition, such as release agents, antioxidants, and ultraviolet (UV) stabilizers. The use of those ingredients, in combination between them, provides a polycarbonate with good color stability after processing, improved light transmission and an optimal behavior during extrusion.
Accordingly, there remains a need for thermoplastic compositions that provide good release properties, while maintaining or improving other properties during processing. For example, there remains a need for thermoplastic compositions that have good release properties with lower release forces, improved color stability, and processability by extrusion, while avoiding any surface vibration or plate-out issues. This and other needs are satisfied by the various aspects of the present disclosure.